Ralph Nader's renegade Green Party presidential campaign is turning out to be an unexpected problem for Al Gore's presidential bid in key Democratic states in the Northeast and West Coast, and could influence the outcome in Midwest battleground states, especially Michigan.

The longtime consumer advocate is demonstrating the potential to fracture Gore's support among core liberal-Democratic constituencies. Such groups as the pro-environment Friends of the Earth are struggling over the question whether to endorse Gore or Nader, and the United Auto Workers has publicly denounced Gore while lavishing praise on Nader.

For the presidential campaign of Texas Gov. George W. Bush (R), all this is manna from political heaven.

"In any state where the election is close, Nader, if he just gets a few percentage points, means a net loss of two or three points for Gore," said a Bush strategist, who was still cautious not to exaggerate Nader's potential at this early stage in the contest.

"He helps us the most in California," a "must-win" state for Gore, he added. Without Nader, California is widely viewed as leaning strongly toward the presumptive Democratic nominee, but with him, "Nader makes us competitive in California," the Bush strategist said.

While running at 4 percent to 5 percent in most national polls, Nader, with his hard-line environmental message, draws support at 9 to 10 percent in California, and 7 percent in Oregon. At those levels, because most of Nader's support comes from voters who would otherwise likely back Gore, Nader could convert the Pacific Coast from a part of the Democratic base to a costly, competitive arena, forcing Gore to spend time and money defending himself in a region expected to be securely Democratic.

Nader, who has been traveling the country on commercial airlines at a hectic pace, has been far tougher on Gore than Bush. On the stump and in interviews, he portrays the Democrat as a sellout to corporate America, lacking backbone and ideals.

In an interview, Nader said there is a clear logic behind his sharp criticism of Gore. "If you can't rely on the so-called liberal party," he said, "it's really all over." Nader said his decision to enter the race was driven "by the inexhaustible collapse of the Democratic Party in every conceivable fashion."

Asked on NBC's "Meet the Press" whether Gore would be any different from Bush, Nader said, "On corporate power issues, apart from the rhetoric, no."

In Maine, describing Gore's role in environmental issues, Nader said: "To use the word 'hypocrisy' is to engage in impermissible understatement."

In a worrisome sign for Gore that he could lose core Democratic support, Stephen P. Yokich, head of the United Auto Workers, issued a statement Tuesday declaring that the UAW is "deeply disappointed" in Gore because he has "tried to have it both ways" on legislation granting permanent normal trade relations with China. "Gore is holding hands with the profiteers of the world," Yokich said.

Nader, Yokich added, "will take a stand based on what is right, not by what big money dictates."

Yokich's comments are significant because the core of the UAW's strength is in Michigan. Analysts for both the Bush and Gore campaigns identify Michigan as one of a few states that could determine the outcome of the election. In Michigan, the UAW is the largest union, and virtually every Democrat running statewide seeks its support. Every UAW vote Nader takes from Gore increases Bush's chances in the state.

In Ohio, another battleground state, Nader is at 4 percent, the Ohio Poll at the University of Cincinnati shows. But in a signal of his potential to raise his numbers, Nader has the highest voter favorability rating among the candidates, including Bush, Gore and Patrick J. Buchanan of the Reform Party.

Nader's favorable rating compared with Buchanan's could prove really important, suggesting that voters determined to vote against major party candidates would be more easily drawn to Nader than Buchanan.

Bush strategists, in addition, are preparing to use Nader as a bargaining chip in negotiations over the fall presidential debates. If Gore aides press for the inclusion of Buchanan, who currently takes more votes from Bush than Gore, the Bush negotiators will demand that Nader be included. "If Gore demands three, then we'll insist on four," the Bush aide said.

As to whether the Gore campaign is concerned about any of this, especially losing support from environmentalists and labor, spokesman Doug Hattaway said, "We are not taking their support for granted, but, at same time, we are not quaking in our boots about Ralph Nader. The real choice in the election is between Al Gore and George Bush; and Al Gore is clearly the better choice."